Rotary seal vane-type pneumatic motors are used extensively in industry as these units have a high power-to-weight ratio. The seal in these motors is accomplished by rotating vanes pressing against the inside surface of a housing, which causes wear and loss of energy due to the rubbing action. Heat generated by this rubbing action is dissipated by directing oil laden air radically through the sides of the housing.
U.S. Pat. No. 2,918,877 to Woodcock discloses a vane-type pump with a rotatable ring as the pressure chamber and fluid under pressure is directed to that part of the outer periphery of the ring on the pressure side of the pump.
U.S. Pat. No. 2,685,256 to Humphreys shows a rotary pump or motor with successive pressure blocks moving inside a freely rotatable ring supported by an antifriction bearing.